1. Field of the Invention
The invention relates to a cylinder head for a liquid-cooled internal combustion engine with several cylinders, comprising at least one intake port and at least two exhaust ports per cylinder, at least one first cooling chamber adjacent to a fire deck and at least one second cooling chamber adjacent to the first cooling chamber, with the second cooling chamber extending over several cylinders. The invention further relates to a cylinder head for several cylinders, comprising an intake side with at least one intake valve and at least one intake valve seat per cylinder and an exhaust side with at least two exhaust valves and at least two exhaust valve seats per cylinder, a parallel or twisted valve image, a central cooling chamber which is flowed through substantially in the longitudinal direction of the cylinder head, with a cooling duct being provided in the area of the exhaust valve bridge between the exhaust valve seats.
2. The Prior Art
A cylinder head for a liquid-cooled internal combustion engine with several cylinders is known from WO 2005/042955 A2, which cylinder head comprises a first cooling chamber adjacent to a fire deck and a second cooling chamber adjacent to the first cooling chamber, with first and second cooling chamber being flow-connected with each other through at least one transfer opening per cylinder. The first cooling chamber can be connected via at least a first opening with a cooling jacket of the cylinder housing. The second cooling chamber comprises a second opening on at least one face side. In order to improve cooling in thermally highly loaded regions, at least a first opening and at least a transfer opening are arranged in the region of a transversal engine plane which is arranged normally to the crankshaft between two adjacent cylinders, with a longitudinal wall being arranged in the first cooling chamber in the area between two exhaust port openings of adjacent cylinders and a coolant duct between the exhaust ports in the area of the exhaust port openings of a cylinder each. The first cooling chamber is arranged continuously for all cylinders.
Two different flow concepts are known in the case of liquid-cooled cylinder heads. In the case of longitudinal flow concepts, the cylinder head is flowed through substantially in the longitudinal direction from one cylinder to the next one. This allows optimal cooling of the valve bridges along the internal combustion engine. It is disadvantageous that relatively high pressure losses will accumulate and that the temperature of the coolant will rise successively from the first to the last cylinder.
Cylinder heads with cross-flow concepts comprise one coolant inlet and one coolant outlet per cylinder, so that each cooling chamber can be flowed through by coolant in the transversal direction to the longitudinal axis of the engine. The cooling chambers of the cylinders are flowed through in parallel here, so that only low pressure losses will occur. The same applies to the valve bridges along the engine. The coolant flow will split up here between the outlet ducts into usually two parts, as a result of which the flow rates are limited. A further advantage is that the inflow temperature of the coolant is the same for all cylinders. Cylinder heads with cross-flow cooling must be equipped with a coolant collector.
A parallel valve image means in this connection that the axes of the intake and/or exhaust ports will open up planes which are arranged parallel to the longitudinal axis of the cylinder head. In contrast to this, the planes opened up by the axes of the respective valves are arranged inclined to the longitudinal axis of the cylinder head in the case of a twisted valve image.
In the case of cylinder heads with cooling chambers which are scavenged longitudinally, the problem may occasionally occur that thermally highly loaded regions which are oriented transversally to the direction of the engine, especially between the valve seats of the exhaust ports in a parallel valve image, can be cooled only insufficiently due to lack of a pressure difference that drives the flow. This may lead to material failure induced for thermal reasons.
It is the object of the invention to avoid these disadvantages and to improve the cooling in a cylinder head of the kind mentioned above. It is a further object of the invention to improve the evenness of cooling between all valve bridges. Flow losses should be kept as low as possible in combination with optimal cooling effect.